The present application relates generally to reconstruction methods for magnetic resonance (MR) image data.
UNFOLD is a method disclosed in U.S. Pat. No. 6,144,873 to Madore et al., which is herein incorporated by reference, for data encoding to improve temporal resolution in magnetic resonance imaging. UNFOLD can provide an acceleration rate of nearly 2. Parallel imaging forms a family of methods that also aim at improving temporal resolution in MRI. SMASH and SENSE are examples of parallel imaging methods.
It has previously been proposed to combine the methods of UNFOLD with SENSE or SMASH in the publication entitled Method for Combining UNFOLD with SENSE or SMASH, 8 PROC. INTL. SOC. MAG. RESON. MED. 1507 (2000) by Peter Kellman and Elliot R. McVeigh. When the UNFOLD method is combined with SENSE or SMASH, acceleration is nearly doubled compared to using SMASH or SENSE alone. With the disclosed method, however, the dynamic portion of the field of view (FOV) is typically constrained to one quarter of the FOV. Thus, the remaining three-quarters of the FOV typically cannot display fully dynamic features of the image sought to be viewed. In contrast, the present method provides high temporal resolution to a region twice bigger; i.e., half the FOV.
One embodiment of the invention is a method for combining an UNFOLD technique with a parallel MR imaging technique to obtain of an object an MR image having a one-half dynamic portion. The method includes (a) obtaining k-space information about the object at a first time point and a first set of k-space locations; (b) obtaining k-space information about the object at a second time point and a second set of k-space locations, wherein at least one of the k-space locations in said second set is not contained in said first set, (c) obtaining information for images at the first and the second time points using the first and the second sets of k-space data, respectively, said images containing spatially aliased and non-aliased components, the image having image pixels; (d) decomposing time variations of one of the image pixels into its frequency content; (e) for a predetermined frequency of the frequency content, using a parallel imaging technique to separate the aliased and the non-aliased components that are overlapped; (f) repeating step (e) for a plurality of frequencies; and (g) repeating steps (d) through (f) for a plurality of image pixels.
An advantage of one or more embodiments of the invention include combining the MRI techniques of UNFOLD with parallel imaging while retaining one-half of a dynamic field of view and obtaining an acceleration nearly twice higher than would be obtained with parallel imaging alone.